声级计 - 噪声计

Brüel & Kjær的声级计和分析仪为1级测量精度,其设计体现了易用性和前所未有的灵活性。 并且,B&K最新一代的声级计可以通过智能手机直接控制,结合扩展功能的应用程序,您可以针对几乎任何测量任务自定义您的声级计。

60多年前,Brüel & Kjær发明了世界上第一台便携式声级计。直到今天,我们仍然引领行业。

B&K 2245 声级计
配备Noise partner

B&K 2245声级计是专门针对噪声测量任务的解决方案,简单易用。 该仪器附带了一系列的应用程序,每个应用程序经过量身定制,可为您的特定工作提供帮助。

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B&K 2250型和2270型
声级计/分析仪

B&K 2250型和2270型声级计的设计基于对技术人员、工程师和顾问的充分研究,并且屡获殊荣,可满足苛刻的测量任务。

 

2250型声级计是单通道仪器,而2270型声级计具有双通道,可同时进行声音和振动测量。

什么是声级计?

声级计是一种与人耳大致相同的方式响应声音的仪器。使用声级计的 目的是对声压级进行客观、可重复的测量。

声级计和噪声计通常用于描述同一种仪器。 在谈到声级计时,主要区别在于精度的分类(由国际标准定义)。 当然,所有Brüel & Kjær的声级计都符合最高的国家标准和国际标准。

了解更多基础声学术语的定义,请查看声学和振动术语表

如何使用声级计

B&K的声级计可用于各种行业和应用,例如:

多年来,Brüel & Kjær创建了丰富的入门和进阶指南,涵盖了几乎所有与声学和振动测量相关的主题。 作为一家公司,我们热衷于分享知识,因此,我们收集整理了这些知识,免费供您下载。

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Time weighting specifies how the SLM reacts to changes in sound pressure. It is an exponential averaging of the fluctuating signal, providing an easy-to-read value.

The analyzer applies Fast, Slow and Impulse (or ‘F’, ‘S’ and ‘I’) time weightings, which are the required weightings according to most international and national standards and guidelines. Environmental assessment standards usually specify which time weighting to use.


Time Weighting
The signal is processed through the weighting filters, and the resulting sound pressure level is displayed in decibels (dB) referenced to 20 μPa on the analyzer’s screen. The sound pressure level values are updated at least once per second.

Assessing a fluctuating noise level means getting a value for a level that is, in simple terms, the average level. The ‘equivalent continuous sound level’, Leq, is known around the world as the essential averaged parameter.

Leq is the level that, had it been a steady level during the measurement period, would represent the amount of energy present in the measured, fluctuating sound pressure level. It is a measure of the averaged energy in a varying sound level. It is not a direct measure of annoyance, though extensive research has shown that Leq correlates well with annoyance.

Leq can be measured directly with most professional sound level meters, and is sometimes called an integrating sound level meter. If an A-weighting filter is used, it is expressed as LAeq, the measurement of the equivalent continuous sound level using the A-weighted filter network
Frequency weighting adjusts how the sound level meter responds to different sound frequencies. This is necessary because the human ear’s sensitivity to sound varies according to the sound’s frequency.

IEC 61672-1 (international standard) defines frequency weightings A, C and Z, but other frequency weightings are occasionally used in specialized applications.
Frequency Rating

A-weighting – dBA/dB(A)
A-weighting adjusts a signal in a way that resembles the human ear’s response at medium-range levels. It is based on the 40 dB equal loudness curve. The symbols for the noise parameters often include the letter ‘A’ (for example, LAeq) to indicate that frequency weighting has been included in the measurement.

A-weighting is required for nearly all environmental and workplace noise measurements and is specified in international and national standards and guidelines. A-weighting filters cover the full audio range, 10 Hz to 20 kHz.

C-weighting – dBC/dB(C)
The response of the human ear varies with the sound level. C frequency weighting corresponds to the 100 dB equal loudness curve, that is to say, the human ear’s response at fairly high sound levels.

C-weighting is mainly used when assessing peak values of high sound pressure levels. It can also be used, for example, for entertainment noise measurements, where the transmission of bass noise can be a problem.

Z-weighting – dBZ/dB(Z)
‘Zero’ frequency weighting is a flat frequency response between 10 Hz and 20 kHz ±1.5 dB excluding microphone response.

Today, the A-weighting network is the most widely used frequency weighting. C-weighting does not correlate well with subjective tests because the equal loudness contours were based on experiments which used pure tones — and most common sounds are not pure tones, but very complex signals made up of many different tones.

When more detailed information about a complex sound is required, the frequency range from can be divided up into sections or bands. This is done with electronic or digital filters, which reject all sound with frequencies outside the selected band. These bands usually have a bandwidth of either one octave or a third of an octave.

An octave is a frequency band where the highest frequency is twice the lowest frequency. For example, an octave filter with a centre frequency of 1 kHz admits frequencies between 707 and 1414 Hz but rejects all others. (The name octave stems from the fact that an octave covers eight notes of the diatonic musical scale). A third octave covers a range where the highest frequency is 1.26 times the lowest frequency.
Frequency analysis
The process of thus dividing a complex sound is termed frequency analysis and the results are presented on a chart called a spectrogram.

After the signal has been weighted and/or divided into frequency bands, the resultant signal is amplified, and the Root Mean Square (RMS) value determined in an RMS detector. The RMS is a special kind of mathematical average value. It is of importance in sound measurements because the RMS value is directly related to the amount of energy in the sound being measured.
International standards are important either because they are used directly or because they provide inspiration or reference for national standards. There are two main international bodies concerned with standardization.
 
The International Organization for Standardization (ISO) deals primarily with methodology to ensure that procedures are defined to enable comparison of results. The International Electrotechnical Commission (IEC) ensures that instruments are compatible and can be interchanged without major loss of accuracy or data.

IEC 61672
“IEC 61672 – Electroacoustics – Sound level meters” is the current international standard that sound level meters should meet to satisfy most modern regulations. It specifies “three kinds of sound measuring instruments” - the “conventional” sound level meter, the integrating-averaging sound level meter, and the integrating sound level meter.

The standard is published in three parts:
  • Part 1: Specifications: Requirements for sound level meter performance and functionality for class 1 and class 2 sound level meters
  • Part 2: Pattern evaluation tests: Details of the tests necessary to verify conformance to all mandatory specifications given in IEC 61672-1. Used by test laboratories to ensure that instruments meet manufacturers claims.
  • Part 3: Periodic tests: Procedures for periodic testing of sound level meters conforming to the class 1 or class 2 requirements of IEC 61672-1:2002
It defines the basic terminology including the central Rating Level parameter and describes best practices for assessing environmental noise.

ISO 1996: ASSESSMENT OF ENVIRONMENTAL NOISE

ISO 1996 is a central standard within environmental noise assessment, acting as a reference work on the subject and commonly referred to by regional standards and regulations.

The standard is in two parts:
  • Part 1 (2016): Basic quantities and assessment procedures
  • Part 2 (2017): Determination of sound pressure levels
Calibration is an adjustment of your sound measuring instrument to measure and display correct values. The sensitivity of the transducer, as well as the response of the electronic circuitry, can vary slightly over time or could be affected by environmental conditions such as temperature and humidity. 

While you are unlikely to ever experience a large drift or change in sensitivity, it is nevertheless, good practice to regularly check the calibration of your measuring instrument before and after each set of measurements. This is best done by placing a portable acoustic calibrator directly over the microphone, providing a precisely defined sound pressure level to which the sound level meter can be adjusted.

In addition to checking calibration before and after measurements, many regulations and standards governing sound level measurements often also require that your sound level meter is calibrated in a laboratory once every 12 or 24 months.